1. Field of the Invention
This invention relates in general to electrical switches and more particularly to cam actuated switching devices.
2. Description of the Prior Art
Essentially all telephone instruments include a switch that is actuated by the removal of the telephone handset from and replacement of the handset on the telephone base. Basically, the actuation of the switch serves to connect the telephone to an associated telephone line responsive to the removal and to disconnect responsive to the replacement of the handset. This switch is therefor often referred to as the line switch or hookswitch. Nearly all hookswitches, however, perform functions in addition to the basic one. Consequently, they generally include between four and six contact pairs that are operated in a particular sequence.
With the advent of modern electronic key telephone systems a host of new features and services are being offered the telephone subscriber that were never economically possible before. To help perform these new functions it is desirable to have a compact hookswitch with a large number of spring combinations. The conventional method of hookswitch operation has been one of "pressure-make" contact actuation. That is, the operation of the hookswitch plunger deflects spring members and causes their contact to be forced together thereby making an electrical contact. In the case of break contact pairs their springs are forced apart thereby opening the electrical connection. With the "pressure-make" type of contact actuation the force required to operate the hookswitch increases dramatically as the number of spring combinations increase.
The force necessary to operate the hookswitch plunger and thus the hookswitch itself is derived from the weight of the telephone handset and over the years not only has the weight of the handset been reduced but telephone base designs have been reduced where only a portion of the handset weight is applied to the hookswitch. Thus hookswitches have had to be designed that operate in response to smaller and smaller forces.
The large force buildup in the hookswitch springs limits the number of spring combinations that can possibly be operated by the weight of the telephone handset and can also result in contact bounce during hookswitch restoral.
One such hookswitch is described in U.S. Pat. No. 4,046,980 to F. A. Rosebrock issued Sep. 6, 1977. The switch as taught by Rosebrock is limited by the fact that it teaches only up to six make or break contact pairs or three transfer "sequence or continuity" contacts as possible with this design. Increasing the amount of contacts actuated by the cam would thus increase the force needed to operate the contacts and defeat its intended purpose.
Therefore, it is an object of the present invention to provide a simple, effective, cam actuated switching device able to switch a large number of contacts with a relatively small force.